Helpful Tool: RESTClient helps test and troubleshoot a variety of HTTP communications
We at Constant Contact have been using Wiztools.org's RESTClient to help us troubleshoot problems with people's code. In particular, if you are receiving a response of '400' from the API, it is likely due to the structure of your XML. This tool is an easy place to GET, edit, PUT and POST XML to various APIs.
RESTClient is a Java platform client application to test RESTful webservices. It can be used to test a variety of HTTP communications.
For more information go here:
Dave Berard Senior Product Manager, Constant Contact